The relationship between TiN microstructures and diffusion barrier properties of TiN against Cu was investigated. TiN deposited by a chemical vapor deposition (CVD) method is composed of columnar grains grown normal to the sidewall on the side of the trench. On the other hand, the grain boundaries of sputter-deposited TiN tilt upward from the normal direction to the sidewall, and the tilt angle depends on the sputtering conditions. Voids between TiN grains are observed on the side of the trench and the size of the voids depends on the deposition conditions. In the Cu/CVD-TiN (the upper/lower layer) and Cu/conventional sputtered TiN system, no Cu is detected in surrounding SiO2 films either outside the sidewall or underneath the bottom of the trench after annealing at 400 degrees C for 3 min. However, in the Cu/long-throw sputtered TiN system, where TiN is composed of columnar grains with void regions between grains, and the tilt angle of the grain boundaries from the normal direction to the sidewall is 27 degrees, some Cu is detected outside the sidewall, even when the TiN thickness on the side of the trench is equal to or thicker than that of CVD-TiN or conventionally sputtered TiN. The diffusion barrier property of TiN in Cu metallization depends on the TiN grain structures rather than on the TiN thickness on the side of the trench.